Several years ago I met someone who attended one of the IAPP conventions. He said a guy there had an RB67 modded to shoot pans, just what you are thinking of. But I don't have any details at all, and I've never searched online so see if there is any posted information.
You might find this blog interesting: http://somakray.blogspot.com/2011/03...-camera-i.html
The late Jim Lipari converted quite a few different 35mm cameras to rotating pan camera. You might search for information on his work for ideas.
To me, the best part of using an RB67 for a conversion is lots and lots of cheap used equipment to experiment with.